1. Field of the Invention
The present invention relates to a sheet stacking apparatus on which a sheet received from an image forming apparatus body is stacked, a sheet processing apparatus, and an image forming apparatus. More specifically, the present invention relates to a sheet stacking apparatus which has a lifting and lowering mechanism of a sheet stack tray.
2. Description of Related Art
In recent years, the number of image forming apparatuses, such as a copying machine or a printer, which can be coupled to a sheet processing apparatus capable of selectively subjecting an image formed sheet to postprocessing such as stapling, has increased. These sheet processing apparatuses can lift and lower a sheet stack tray.
The tray is integrated with a driving member and is lifted and lowered by a pinion in the driving member and a rack provided in the apparatus. The tray is coupled to a belt and is lifted and lowered by a pulley (see Japanese Patent Application Laid-Open (JP-A) Nos. 2006-256732, and 2003-95527)
As described above, the lifting and lowering tray in the related art is of a rack & pinion type or a belt & pulley type for phase alignment of right and left rails as well as rails on both sides of a frame for supporting the load of the tray. The lifting and lowering tray need to be assembled and maintained while the installing posture of the apparatus in the used state is held. Since the operating procedure and the operating space are limited, there exist the following problems.
In the rack & pinion type described in JP-A No. 2006-256732, the tray which is integrated with the driving member is assembled to the rack extended in the lifting and lowering direction from above the apparatus in the used state. A space is required outside the lifting and lowering movement region (above or below the rack) during assembling.
Also in the belt & pinion type described in JP-A No. 2003-95527, the tray is guided by guide channels, extended in the lifting and lowering direction, which are formed in a front surface of a stacking wall from above the apparatus in the used state. The assembly properties and the maintenance properties are poor. Further, the member which couples the stack tray to the raising and lowering driving member is fixed to the belt. Phase alignment is necessary.